The present invention generally relates to facsimile transmission systems, and more particularly to a facsimile transmission system which uses an image memory of a facsimile machine.
Owing to the popular use of facsimile machines, there are now variety of usages of the facsimile machines. As a result, there are demands to increase the functions of the facsimile machines.
For example, there are demands to make it possible for the operator to take home a document which is to be transmitted and to make it possible to program a facsimile transmission so that the operator need not attend the facsimile machine when actually making the facsimile transmission. In order to satisfy such demands, there is a proposed facsimile machine which is provided with an image memory for storing image data of the document which is to be transmitted.
In the facsimile machine which is provided with the image memory, the image data of the document which is to be transmitted is temporarily stored in the image memory and the stored image data can be automatically transmitted at an arbitrary time. After the image data of the document is stored in the image memory, the document no longer needs to be set on the facsimile machine and the operator can freely take home the document. In this specification, a mode of the facsimile machine in which the image data of the document is temporarily stored in the image memory and transmitted at an arbitrary time will hereinafter be referred to as a store-and-forward mode.
Of course, it is desirable that the memory capacity of the image memory provided in the facsimile machine is as large as possible. However, an upper limit of the memory capacity is determined by a maximum permissible cost of the image memory for use on the facsimile machine.
In the store-and-forward mode of the facsimile machine, the image memory may run out of available empty memory area while the document is being read. In this case, the image data up to the previous page is regarded as the effective data and an error information is output. This error information indicates that the image data related to the present page which is being read cannot be stored in the image memory. In this case, the present and subsequent pages are set on the facsimile machine for transmission after the pages stored in the image memory are transmitted.
However, the conventional facsimile transmission system detects an error and discontinues the transmission process when the image memory runs out of available empty memory area while the document is reading the present page of the document. As a result, there are problems in that the present and subsequent pages of the document must be set again on the facsimile machine after the transmission of the stored pages up to the previous page of the document is completed, and the operator on the transmitting station must carry out the troublesome operation of setting again the present and subsequent pages of the document on the facsimile machine. On the other hand, at the receiving station, pages of an unrelated document may be received between the previous page and present pages of the document because the previous page and the present page are transmitted from the transmitting station at different times. For this reason, there is a problem in that a disorder of the pages of the received document may occur at the receiving station when the above described error occurs at the transmitting station.